September 27th, 2017
Purpose: To see the relationship between cell size and diffusion of materials.
· Phenolphthalein agar
· 0 .1M sodium hydroxide (NaOH) solution
· Scalpel or knife
· 400-ml beaker
· Safety goggles.
In this lab, blocks of phenolphthalein agar were used to imitate and demonstrate the properties of cells and its ability to move materials into and out of its membrane. This lab helped visualize and recreate the process of a passive transport system whereby cells can move small particles through the lipid bilayer of its cell membrane. This passive process is known as diffusion. Diffusion is a passive process as it requires no energy to move the materials around. The particles can freely enter and exit the membrane in the presence of a concentration gradient, albeit in a random fashion; as the movement of particles in diffusion are random. A concentration gradient occurs when one area contains a higher concentration of a substance and a lower concentration in another. This allows for particles to diffuse from areas of high concentrations to low concentrations, until the concentration gradient reaches equilibrium.
Three differently sized blocks of agar were placed in a sodium hydroxide solution to allow for the solution to diffuse into the blocks. This allowed for different results between the blocks as they had different densities and had either a higher or lower number of particles per unit volume. The blocks were then cut open and measurements were recorded. By observing the coloured areas inside of the blocks, it showed the extent of diffusion of the solution into the cubes.
The blocks of agar were composed of phenolphthalein, a commonly used compound as a pH indicator in acid-base titrations. The properties of phenolphthalein enable it to turn solutions pink when exposed to an alkaline solution. The phenolphthalein modelled the diffusion of materials out of the cells whereas the sodium hydroxide solution represented the diffusion of materials into a cell. Although there are multiple factors that can affect diffusion, namely temperature, concentration and pressure – this lab focused primarily on density, as it modeled the effect that cell size can have on diffusion.
Data Table 1. The calculated results for the total volume of the cube, the uncoloured area, the coloured area. Also included: Volume of Coloured Area/Total Volume of Cube and Percentage of Cube NaOH diffused.
Intended Total Volume of cube (cm3)
Actual Total Volume of cube (cm3)
Volume of Uncoloured Area (cm3)
Volume of Coloured Area(cm3)
Volume of Coloured Area/Total Volume of cube
Percentage of cube NaOH(aq) diffused
Sample Calculations (done with cube 3)
Calculating the Actual Volume of the Cube
Calculating the Volume of the Uncoloured Area
Calculating the Volume of the Coloured Area
Calculating the Ratio...